In many cases, it is important to be able to inject intravenously a discrete quantity of liquid rapidly into a patient. It is also important that mixing of the discrete quantity of liquid with the patient's blood and/or a driving liquid, should be kept to a minimum. For example, certain drugs, such as, anaesthesiology drugs may cause damage to the peripheral veins. Thus, it is important where such drugs are injected into a peripheral vein, the injection should be delivered through the peripheral vein into the main blood pool of the patient as quickly as possible.
Another case in which it is essential that a discrete quantity of liquid be injected rapidly into a patient, is in the case of a bolus injection where a radionuclide liquid is injected intravenously and is directed to, for example, the heart or other organ to enable nuclear imaging or counting to be made. It is particularly important that the discrete quantity of radionuclide should be delivered to the heart with the minimum amount of mixing with the blood or the driving liquid used with the bolus. Where mixing takes place, it will be appreciated that the imaging or counting will be much less clear and the counting of lower statistical significance than where the fluid is retained in a discrete quantity.
In general, bolus injections are delivered by pushing the radionuclide liquid through the venous system with a driving liquid. A typical driving liquid is a saline solution. One way of doing this is to connect an intravenous needle to one port of a three-way valve. The other two ports are respectively connected to a syringe in which the bolus radionuclide liquid is stored, and a second syringe in which the driving liquid, generally saline solution, is stored. The valve is set initially so that the first syringe with the radionuclide is connected to the intravenous needle, and the radionuclide is dispensed from the syringe through the intravenous needle. The valve is then immediately switched over to connect the saline solution syringe to the intravenous needle, and the radionuclide is then flushed through the veins by delivering the saline solution rapidly from the syringe into the vein.
Unfortunately, this technique is cumbersome, and in general requires two people to operate it, one to operate the radionuclide syringe, and the other to operate the driving fluid syringe. Another very important problem that arises with this technique is that it is extremely difficult to have the saline solution following immediately after the radionuclide liquid, and thus mixing of the radionuclide with the blood occurs very often before the saline solution is delivered into the vein. Furthermore, it has been found in the past that using this technique also causes undesirable mixing between the radionuclide liquid and the saline solution. Thus, by the time the radionuclide is delivered to the organ which is being examined, in general the heart, it has mixed considerably with both the blood and the saline solution, and thereby accurate nuclear imaging cannot be achieved.
Another known device for delivering a bolus injection is disclosed in U.S. Pat. Specification No. 4,364,376. This device comprises a bolus retainer which is essentially a cylindrical member which forms a chamber in which the bolus liquid is stored. A needle is attached to one end and a valve is attached to the other end. A syringe is initially connected to the valve and the valve is opened to the bolus chamber. Radionuclide is then drawn into the bolus chamber, and the valve closed. A syringe is then filled with a driving liquid generally saline solution, and reconnected to the valve. The valve is then opened and the driving liquid is pumped into the bolus chamber, which in turn delivers the bolus and driving liquid into the patient's vein. The problem with this device is that the bolus chamber tends to be relatively long, and thus leads to a very cumbersome device. This is a particular problem, since it is generally necessary to shield the bolus chamber with a heavy lead radiation shield to protect the doctor or nurse from radiation. Thus, this is an extremely awkward device to handle, and because of this, can cause the needle to move around in the patient's arm, thereby causing considerable pain and discomfort, and in many instances can cause the needle to project right through the vein and into tissue. This, it will be appreciated, is a very serious problem. A further disadvantage of this device is that because of the construction of the bolus chamber, it has been found that considerable mixing of the bolus liquid and the driving liquid takes place in the chamber. Thus, by the time the radionuclide reaches the patient's heart it is well diluted and nuclear imaging is most inaccurate.
There is therefore a need for a device which overcomes the problem of known devices for delivering bolus injections, as well as known devices for delivering any discrete quantity of liquid into the body.